1. Field of the Invention
This invention relates to three-channel (stereo plus mono) audio signal transmission or conveyance systems and to three-component (stereo plus back) sound reproduction systems.
2. Description of the Prior Art
There are several known systems which convey, on three channels (LC, RC, MC), left and right stereo signals (LS,RS) and a mono signal (MS=LS+RS), such as terrestrial television systems with "NICAM"728 stereo and frequency modulated (FM) mono, and "Video 8" systems with pulse code modulated (PCM) stereo and FM mono. There is also known a system of sound reproduction using three sources which produce left and right stereo signals (LS,RS) and a background or "back" signal (BS), these signals subsequently being used to reproduce left and right stereo sounds and a back sound.
The present invention is concerned with reproducing three-component stereo/back signals conveyed using a three channel stereo/mono system. A simple way of doing this would be to convey the left and right stereo signal components (LS,RS) on the left and right stereo channels (LC,RC), respectively, and to convey the back signal component (BS) on the mono channel (MC). However, this presents a problem that mono compatibility is lost, because a mono receiver would receive merely the back signal (BS), whereas for satisfactory mono reproduction the reproduced mono signal should primarily be the sum of the left and right signals (LS+RS).